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The Mustang 345 and Its Mechanical Legacy
The Mustang 345 skid steer loader is a compact, maneuverable machine designed for light to medium-duty construction, landscaping, and agricultural work. Manufactured by Mustang Manufacturing Company, a brand with roots dating back to the 19th century and later acquired by Manitou Group, the 345 was part of a generation of machines that emphasized mechanical simplicity and rugged performance. Though no longer in production, many units remain in use due to their straightforward design and ease of repair.
The 345 uses a dual hydrostatic drive system powered by hydraulic pumps and motors. Each side of the machine is independently driven, allowing for zero-radius turns. The drive motors are typically radial piston or gear-type hydraulic motors, and in this case, the unit in question uses a Sperry Vickers motor—an older but respected brand in hydraulic components.
When One Drive Motor Fails
A common issue in aging skid steers is the failure of one drive motor, resulting in the machine only moving forward and backward but not turning. This behavior is often misunderstood. Even if one motor is functional, the machine may not pivot or "doughnut" if the opposite side is mechanically disconnected—such as when a drive chain is missing. In a skid steer, turning requires one side to resist or reverse while the other moves forward. Without a chain connecting the motor to the wheels, the system cannot generate the necessary resistance, and the machine will simply roll straight.
Terminology Explained
Swapping drive motors from one side to the other is a common diagnostic method, but it carries risks. If a motor is internally damaged and contaminated with metal shavings, transferring it to the other side can spread debris into the hydraulic system. Since many older machines lack filtration between pumps and motors, this contamination can quickly damage the pump—a component that can cost upwards of $6,000 compared to $1,000 for a lift pump.
A safer approach involves:
If a motor is confirmed faulty, the decision to rebuild or replace depends on availability and cost. Rebuilding typically costs around $900, but sourcing parts for older Sperry Vickers models can be difficult. If parts are unavailable, consider looking for compatible motors used in other machines or retrofitting a modern equivalent.
Lessons from the Field
One operator learned the hard way about the importance of hydraulic cleanliness. After removing a motor without capping the hoses, over $100 worth of hydraulic fluid spilled onto the shop floor. This not only created a mess but introduced air and potential contaminants into the system. Always use proper caps and plugs when disconnecting hydraulic lines.
Ride Control and Modern Enhancements
Some aftermarket kits offer ride control systems for skid steers, using electric valves and accumulators to smooth out the ride over rough terrain. These systems can increase productivity by up to 27% in load-and-carry applications, reducing operator fatigue and material spillage. While not standard on older machines like the Mustang 345, such upgrades can be retrofitted with the right expertise.
Conclusion
Working on older skid steers like the Mustang 345 requires a blend of mechanical intuition, patience, and access to legacy parts. Understanding the interplay between hydraulic systems, mechanical linkages, and drive components is essential for effective troubleshooting. With careful diagnostics and preventive practices, even decades-old machines can be brought back to life and continue serving on job sites for years to come.
The Mustang 345 skid steer loader is a compact, maneuverable machine designed for light to medium-duty construction, landscaping, and agricultural work. Manufactured by Mustang Manufacturing Company, a brand with roots dating back to the 19th century and later acquired by Manitou Group, the 345 was part of a generation of machines that emphasized mechanical simplicity and rugged performance. Though no longer in production, many units remain in use due to their straightforward design and ease of repair.
The 345 uses a dual hydrostatic drive system powered by hydraulic pumps and motors. Each side of the machine is independently driven, allowing for zero-radius turns. The drive motors are typically radial piston or gear-type hydraulic motors, and in this case, the unit in question uses a Sperry Vickers motor—an older but respected brand in hydraulic components.
When One Drive Motor Fails
A common issue in aging skid steers is the failure of one drive motor, resulting in the machine only moving forward and backward but not turning. This behavior is often misunderstood. Even if one motor is functional, the machine may not pivot or "doughnut" if the opposite side is mechanically disconnected—such as when a drive chain is missing. In a skid steer, turning requires one side to resist or reverse while the other moves forward. Without a chain connecting the motor to the wheels, the system cannot generate the necessary resistance, and the machine will simply roll straight.
Terminology Explained
- Hydrostatic Drive: A propulsion system using hydraulic fluid to transfer power from the engine to the wheels or tracks.
- Drive Motor: A hydraulic motor that converts fluid pressure into rotational motion to drive the wheels.
- Chain Drive: A mechanical linkage that transfers torque from the motor to the axle or sprocket.
- Sperry Vickers: A legacy brand of hydraulic components known for reliability, now part of Eaton Corporation.
Swapping drive motors from one side to the other is a common diagnostic method, but it carries risks. If a motor is internally damaged and contaminated with metal shavings, transferring it to the other side can spread debris into the hydraulic system. Since many older machines lack filtration between pumps and motors, this contamination can quickly damage the pump—a component that can cost upwards of $6,000 compared to $1,000 for a lift pump.
A safer approach involves:
- Pressure Testing Use hydraulic gauges to measure charge pressure under load and no-load conditions. This reveals whether the motor is receiving adequate pressure and how much internal leakage is occurring.
- Leakage Testing All hydraulic motors have some internal leakage. Excessive leakage indicates worn seals or internal scoring.
- Bench Testing While not ideal without specialized equipment, some basic checks can be done. A motor that cannot be turned by hand may be normal for certain designs, but excessive resistance or grinding suggests internal damage.
If a motor is confirmed faulty, the decision to rebuild or replace depends on availability and cost. Rebuilding typically costs around $900, but sourcing parts for older Sperry Vickers models can be difficult. If parts are unavailable, consider looking for compatible motors used in other machines or retrofitting a modern equivalent.
Lessons from the Field
One operator learned the hard way about the importance of hydraulic cleanliness. After removing a motor without capping the hoses, over $100 worth of hydraulic fluid spilled onto the shop floor. This not only created a mess but introduced air and potential contaminants into the system. Always use proper caps and plugs when disconnecting hydraulic lines.
Ride Control and Modern Enhancements
Some aftermarket kits offer ride control systems for skid steers, using electric valves and accumulators to smooth out the ride over rough terrain. These systems can increase productivity by up to 27% in load-and-carry applications, reducing operator fatigue and material spillage. While not standard on older machines like the Mustang 345, such upgrades can be retrofitted with the right expertise.
Conclusion
Working on older skid steers like the Mustang 345 requires a blend of mechanical intuition, patience, and access to legacy parts. Understanding the interplay between hydraulic systems, mechanical linkages, and drive components is essential for effective troubleshooting. With careful diagnostics and preventive practices, even decades-old machines can be brought back to life and continue serving on job sites for years to come.
